BDNF and major depressive disorder: Because of the key role of BDNF–TrkB signaling in depression (Nestler et al., 2002; Hashimoto et al., 2004; Duman and Monteggia, 2006; Hashimoto, 2010, 2013; Duman and Li, 2012; Lindholm and Castrén, 2014), regional differences in the alterations of BDNF levels in LH and non-LH rats may also contribute to resilience to inescapable stress.